We previously reported an alteration in the biomechanical properties of the posterior sclera of young ADAMTS10-mutant Beagle dogs as compared to age-matched normal dogs prior to the spontaneous inception of open angle glaucoma (Palko et al, IOVS 2013, 54(4)). This study aimed to examine how age affected scleral biomechanical properties in both affected and normal dogs.

Methods

Additional older Beagle dogs were testing resulting in 13 affected and 7 normal in total. The affected older dogs had the same G661R missense mutation in ADAMTS10. Inflation testing was performed in scleral shells to measure the through-thickness strains in the posterior sclera using an ultrasound speckle tracking technique. Dynamic viscoelastic mechanical testing was then performed on dissected posterior scleral strips, following the same protocol as in the young dogs. The association between age and scleral biomechanical properties (complex modulus E* - resistance to deformation, and tan(delta) - viscous damping ability) was evaluated using multivariate linear regression. The correlation between the tangential strains during inflation testing and the complex modulus obtained from strip testing was also evaluated.

Results

In both groups, age was positively associated with complex modulus E* (p<0.001) and negatively associated with tan(delta) (p<0.001), and the regression slopes were similar (Figure 1 & 2). The complex modulus E* was marginally higher in the normal (p=0.066) while no statistically significant difference was found in tan(delta) between normal and affected (p=0.28). E* was negatively correlated with the posterior circumferential tangential strains (R=-0.856, p=0.003).

Conclusions

Age-associated stiffening of the posterior sclera was observed in both the affected and normal Beagle dogs. In addition, both affected and normal dogs showed a significant loss of the mechanical damping ability in the posterior sclera. Although the affected dogs suffered from a prolonged elevation of IOP and were treated with topical prostaglandin drugs, age-associated scleral stiffening was still prominent. In this study, strip testing and inflation testing yielded consistent results. Further analysis of the effect of accumulative IOP and microstructural changes are currently underway.